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Re: Tertiary mammals in the Cretaceaous
On Sat, 22 Feb 1997 John Bois wrote:
> Do you think we will find any other modern-aspect mammals in existence
> befor the K/T?
> Do you think the ones we know about were strictly micro niche animals?
> Do we find burrows anywhere?
As fas as I know, very few mammals which belong to modern orders have
been found in the Cretacous. A primitive primate (?) (Purgatorius)
has been found in North American Latest Cretaceous strata, but it has
been suggested that the few specimens are Paleocene in age
and have been mixed up with Cretaceous material. In addition, it is
not at all sure that the group Plesiadapoidea to which Purgatorius
belongs are indeed primitive primates.
In Australia, two Cretaceous monotremes (which were obviously more
diverse in the Late Cretaceous and Early Tertiary than they are
today) have been found. One of them (Steropodon) is a relative of the
modern platypus, the other one was recently described in Nature and belongs to
extinct group (I can't recall its name).
In South America another primitive ungulate, Perutherium, has been found in a
probably Cretaceous locality (Laguna Umayo). It belongs to a group
(Notoungulata) which flourished in South America during much of the
Tertiary but is extinct today, however it is still a 'modern-aspect'
mammal for the Cretaceous.
In the Cretaceous of Asia primitive placental mammals have been found which are
possibly related to rodents and lagomorphs (rabbits etc.), but I am
not well informed about them. Perhaps someone else knows better
whether they are really their relatives.
As far as I know, the only place on earth where Latest Cretaceous
mammals are well documented is North America (with the Bug Creek
and Harbicht Hill faunas), so it is not at all astonishing that we
know only a handful of mammals of modern aspect. However, I am sure
that more of them were existing and will, as I hope, eventually be
found. The origin of many groups of modern mammals is still unknown or
questionable, but it has been speculated that many of them already
developed in the Cretaceous.
Most of the known animals were small. (The exception are the
Australian monotremes, which were already medium-sized.)
Usually, only their teeth have been found, so we know very little
about what they looked like or how they lived, but I can't imagine
that all of them were nocturnal. I do not know of
any burrows that have been found, but this is not surprising as most
fossils have been found in sediments formed by river channels.